Maybe the trick isn't the amount of benefit for people who are capeable of working, or even accessing work. IMO I think the trick is to get people to want to support themselves and their families, if they are able to (eg. people WITHOUT disabilities that prevent them from working, as there are many people with disablilites who do work and want to work, or those who are saving the country millions of pounds by being under appreciated careers for people with disabilities)
In the Netherlands I believe you are EXPECTED to restart work or retrain to enable you to start work if you have children and are supported financially by the state, when your youngest child reaches school age. Even if this is just to top up the benefits you recieve, or to earn an extra few pounds a week above what you would receive on benefits.
If you don't your benefits are cut - effectively you are fined. You are given help and support to make these changes to your lifestyle, but the EXPECTATION is there that this is YOUR RESPONSIBILITY as an adult eg you should support yourself as an adult and you should support your family if you are at all able to.
Also if you are on benefits, you automatically have a government bank account set up - none of this nonsense with fruity vouchers, as people are expected to be responsible for themselves and manage their benefit money effeciently and they are trusted to make adult, responsible decisions about what they feed their kids etc.
So their model uses a financial incentive (you lose money for non-compliance) plus support to get back to being financially independant, whilst treating benefit claimants as responsible adults - giving them bank accounts and the choice to spend their money as they will.
I do agree that benefits (for able individuals) shouldn't be more than the MODE wage ie the most common wage in the country, which is probably below £25,000, or the dual income minimum wage idea could work.